User list for a Get.
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 Syntax

        GT_GetList(<oGet>,<cType>,<bReturn>,<bValid>, ;
            [<bFind>],[<bFor>],[<nTop>],[<nLeft>]) -> lSuccess

 Arguments:

      <oGet> is the Get Object passed to the post block.

      <cType> is the type of window to use. 'A' uses an
      array list and 'D' uses a Browse on a DBF file.

      <bReturn> block to extract the information to put
      into the Get field. It will be passed the element
      of the array or the record number (current) in the
      Browse case.

      <bValid> the block stating whether the result in the
      Get field is valid.

      <bFind> defines which option to start on. Should
      return a number for 'A' windows or a value to seek
      with the browse. For Browses this will act as a
      while clause against the index.

      <bFor> for clause. Only for Browse lists.

      <nTop> and <nLeft> specify the top left corner of
      the window.

 Returns:

      Logical valid status.

 Description:

      Allow a PostBlock on a get to display the user
      a list of legal options from an array or an open
      datafile. Allows while/for options and displays the
      list on screen. When an option is selected the list
      is removed.
      Requires extra information in :Cargo

 Examples:

      oGet:PostBlock := { | oGet | Suppliers->(Gt_GetList( ;
          oGet, ;                         // Get object
          'D', ;                          // Datafile
          { | | Field->Code }, ;          // Return
          { | cData | DBSEEK(cData) }, ;  // Valid
          { | cData | RTRIM(cData) }, ;   // Seek/while
          { | | Field->Qty > 0 }, ;       // For
          02, ;                           // Top
          02)) }                          // Left

      aGets[01][01]:Cargo := { ;
          {'Code','Supplier'}, ;          // Titles
          {{ | | Field->SuppCode }, ;
              { | | Field->SuppName }}, ; // List fields
          {}}                             // Only used with array


 Source: GT_GETLI.PRG

 Author:  Martin Bryant